Magnetoresistive (MR) read sensors are used in magnetic disk and tape systems to read signals in the form of changes in magnetic flux. Typically, MR read sensors are rectangular multi-layered structures in which thin film layers are deposited on a substrate.
Presently known thin film magnetic heads, known as merged heads, include an inductive write element for recording signals and a magnetoresistive (MR) sensor for reading the recorded signals. Write operations are carried out inductively using a pair of magnetic write poles which form a magnetic path and define a transducing nonmagnetic gap in the pole tip region. The transducing gap is positioned close to the surface of an adjacent recording medium such as a rotating magnetic disk. An electrical coil formed between the poles causes flux flow in the magnetic path of the poles in response to a current in the coil that is representative of signal information to be recorded.
Read operations are carried out by the MR sensor which is spaced from a pair of magnetic shields. The MR sensor changes resistance in response to changes in magnetic flux on the adjacent magnetic medium. A sensing electric current passed through the MR sensor senses the resistance of the MR sensor, which changes in proportion to changes in the magnetic flux.
Conventionally, the MR sensor is electrically isolated from the pair of magnetic shields. A separate set of conductors are provided on one surface of the MR sensor to pass a reference current through the MR sensor in a current-in-the-plane (CIP) mode. However, the CIP mode can create problems such as shorting due to electromigration. Also, a CIP mode MR sensor can be relatively large in size and expensive to mass produce because of its complex construction.
More recently, a compact MR head has been developed in which the magnetic write poles serve also as the shields for the MR sensor and further as a means for conducting the MR sense current. The structure and method of forming such a compact MR head is disclosed in U.S. Pat. No. 5,446,613 "Magnetic Head Assembly With MR Sensors" by Robert E Rottmayer, issued Aug. 29, 1995, which is incorporated herein by reference.
In U.S. Pat. No. 5,446,613, a thin film magnetic head incorporates an inductive write portion including two pole/shield layers and a read portion including a giant magnetoresistive (GMR) sensor. The pole/shield layers are relatively thick and serve as conductive leads which can carry high current with minimal heating and low current density. The GMR sensor defines data track width and thus minimizes off-track reading of data.
Another prior art reference is U.S. Pat. No. 5,576,914, entitled "Compact Read/Write Head Having Biased GMR Element" by Robert Rottmayer et al. issued on Nov. 19, 1996, which is incorporated herein by reference. In U.S. Pat. No. 5,576,914, a compact read/write head is provided having a magnetically biased GMR sensor which provides reduced noise in the read signal and improves the linearity and gain of flux sensing. Biasing of the GMR sensor provides distinguishable response to the rising and falling edges of a recorded pulse on an adjacent magnetic recording medium. Biasing also improves the linearity of the response and helps to reduce noise. The GMR sensor is magnetically biased such that the major domains of alternate GMR layers define a scissor-type configuration when no excitation field is supplied by an adjacent recording medium.
When an excitation field is supplied by the adjacent record medium, it rotates the scissors configuration from a crossed (90.degree.) state towards either a closed (0.degree.) state or an anti-parallel (180.degree.) state, depending on the polarity of the excitation field. The resultant change in cosine (and resistance of the GMR sensor which is a function of cosine) is therefore from zero to a positive one (cosine 90.degree.=+1.0) or to a negative one (cosine 180.degree.=-1.0). The resultant change in resistance of the GMR sensor therefore indicates the polarity of change of the excitation field. A disadvantage of this approach is that the structure is complex and therefore difficult to manufacture.
It is therefore desirable to provide a method and apparatus to bias a GMR current flowing perpendicular through the major plane (Cpp) head using a method that is simple to manufacture and provides an essentially uniform field throughout the sensor.